Effects of Microgravity on Animal-Bacterial Symbioses

Microbes play a significant role in the normal development of animal tissues. In this research project we examine the effects of microgravity on the normal developmental interactions between an animal host and a bacterial symbiont. To examine the effects of the space environment on animal-microbe symbioses we use the model system between the squid Euprymna scolopes and the luminescent bacterium Vibrio fischeri.

To examine the impact of microgravity on this symbiosis a two-pronged approach is used. First the symbiosis is examined under simulate microgravity using rotating bioreactors called high-aspect-ratio rotating wall vessel bioreactors (HARVs). The HARVS provide a low-shear environment for both the host and symbiont, thereby simulating the space environment. Second, a small pilot experiment was flown on the STS-134 shuttle mission to examine the symbiosis under natural microgravity conditions. Our objectives for this project are as follows: to monitor the normal developmental timeline of symbiosis and examine the host immune response under microgravity conditions.

When squid hatch from their eggs they are born without bacteria (aposymbiotic) and must acquire those bacteria from the surrounding seawater. To acquire those bacteria the squid uses specialized ciliated cells on the surface of the light organ. However, only a specific strain of the bacterium Vibrio fischeri is capable of colonizing the squid light organ. Once the bacteria move inside the light organ the squid is considered symbiotic and the V. fischeri induces a developmental remodeling of the host light organ. The ciliated cells used to initiate the sym Squid in Space.m4v biosis die through apoptosis and begin to regress. This developmental restructuring of the light organ (shown here in these micrographs) is essential for the normal development of the host squid.